Mr Hague replied evasively: “I think we have to await the outcome of the Chilcot inquiry before we should try to pass judgement on these events.”

Urging MPs to focus on the present-day situation, he added: “We are not planning in these circumstances a British military intervention in Iraq.”

The Foreign Secretary faced the Commons within hours of US President Barack Obama’s announcement that he was sending up to 275 armed troops to “provide support and security” in Iraq for US embassy staff and other personnel.

Tory MP Robert Halfon voiced concern that reopening the Tehran embassy signalled a “softening” of Britain’s approach to Iran.

Mr Hague denied that, but added: “Iran does have the capability to play a more positive role across the region.”

Britain would work for a wider change in Iran’s foreign policy and for increased links “between the peoples of our countries” while also pursuing negotiations on the country’s nuclear capacity, Mr Hague said.